1. Field of the Invention
The present invention relates to an automatic focusing device for a video camera, an electronic still camera, or the like.
2. Discussion of Background
Solid-state self-scanned image sensors of area configuration with a rectangular light detecting area, such as CCDs, PDAs, and the like have found use as imagers in video cameras and electronic still cameras, for example. Such solid-state self-scanned image sensors of area configuration are capable of producing not only video signals, but also focus signals. An automatic focusing system which operates by relying on a focus signal produced by a solid-state self-scanned image sensor of area configuration is referred to as a frequency detecting system since a high-frequency component of a video signal is detected and a focus signal is generated on the basis of an increase or decrease in the high-frequency component.
The frequency detecting system is however disadvantageous in that it is difficult to determine the direction in which the lens position lies, i.e., to ascertain whether the lens is in a front focus position or a rear focus position, and hence the lens tends to oscillate back and forth across a well focused position. Another problem of the frequency detecting system is that if the object to be imaged is of a low contrast or the position of an image formed by the lens is widely spaced from the imaging surface, then the system is prone to errors because the focus signal remains substantially unchanged when the lens is slightly moved.